1. Field of the Invention
The present invention relates to a method of manufacturing a microstructure such as a barrier lib or a spacer formed at an internal space between two flat panels constructing a flat panel display and, in particular, to a method of manufacturing a microstructure using a photosensitive glass substrate.
2. Description of the Background Art
Recently, flat panel displays (FPD) playing a major role in a man-machine interface, such as liquid crystal displays (LCD), field emission displays (FDD), plasma display panels (PDP), plasma address liquid crystal displays(PALC) are having been actively developed. Each of the above-described flat panel displays commonly includes two flat panels, each being arranged at a certain distance from each other, and a plurality of pixels formed between the two flat panels. In addition, the displays have something in common in that an internal space of the display formed between the two flat panels has to maintain a lower pressure than an external air pressure and the size of the internal spacer has to be maintained constant. For this purpose, it is necessary to manufacture a microstructure member such as a barrier lib or a spacer between the two flat panels, in order to prevent a damage to the panels due to a difference between the pressure in the internal space of the flat panel display and the external air pressure, and maintain the thickness of the internal space constant.
For a method of manufacturing a barrier lib applied to the manufacture of PDP and PALC in this microstructure member, screen printing method, sand blasting method, molding method, etc. are proposed. However, there have been many problems in those methods.
In case of the screen printing method, there is a problem that it takes much time for manufacturing a barrier lib because the method requires a process of repeating printing and drying several times, and it is difficult to form a high definition barrier lib because the shape of the barrier lib is distorted when a screen alignment is not performed well.
In case of the sand blasting method, there is a problem that since a barrier lib is manufactured by abrading the panel using polishing particles, the material of the panel is wasted and accordingly the manufacturing cost is high, and since the panel is shocked by the polishing particles, it is likely to lead a damage to the panel.
The molding method is forming a barrier lib by putting a mold on a semi-solid phased film, a material for the barrier lib, or a paste and applying a uniform pressure to the mold. However, there is a problem that it is difficult to manufacture a barrier lib of an uniform height and separate the mold and the barrier lib because it is difficult to apply a uniform pressure to the mold.
Besides, LIGA (Lithography, Electroplating and Molding), silicon anistrophic etching, photosensitive glass substrate etching, etc. are newly proposed as another method of manufacturing a microstructure.
However, there is a problem that the LIGA requires a high-priced equipment because X-rays has to be generated by the method.
In addition, the silicon anistrophic etching is a method of performing anistrophic etching after forming a mask pattern on a silicon single crystal substrate. However, there is a problem that since it is difficult to etch a large area at an uniform depth, it is difficult to manufacture a microstructure of an uniform height, and since the price of the silicon single crystal substrate is very high, the manufacturing cost is high.
The photosensitive glass substrate etching among the conventional methods of manufacturing a microstructure will now be described in brief.
Firstly, as illustrated in FIG. 1A, a photosensitive glass substrate 2 is prepared. The photosensitive glass substrate 2 is mainly composed of SiO2 and Li2O, including a small amount of CeO2 and Al2O3 and a small amount of photosensitive metals such as Au, Ag and Cu. Besides, other oxides may be included as the needs arise.
Next, as illustrated in FIG. 1B, a mask pattern 4 is put on the photosensitive glass substrate 2, and ultraviolet rays are irradiated on a portion not covered with the mask pattern 4. Generally, the energy for irradiating ultraviolet rays on a photosensitive glass substrate 2 with a thickness of 1 mm is approximately 2J/cm2 when the wavelength of the ultraviolet rays is 310 nm.
In the glass substrate 2 exposed to ultraviolet rays for a predetermined time, as trivalent Ce ions are changed into tetravalent Ce ions at an exposed portion, electrons are released into the glass substrate 2.
Next, the mask pattern 4 on the glass substrate 2 is removed and the glass substrate 2 is heat-treated at a temperature of 350xc2x0 C. for about 30 minutes. The electrons react with photosensitive metal ions at the exposed portion of the glass substrate 2 to thereby deposit metal elements.
Next, the glass substrate 2 from which the metal elements are deposited is heat-treated at a temperature of 570xc2x0 C. for 2xcx9c3 hours. Then, as illustrated in FIG. 1C, crystal phases such as SiO2, Li2O, etc. are formed around metals using the metals as the core at the exposed portion (D1) of the photosensitive glass substrate 2. In other words, the exposed portion (D1) is a mixed structure of amorphous and crystal phases, and the percentage of crystal phases is about 25%. Meanwhile, an unexposed portion has an amorphous structure.
Next, when the glass substrate 2 is dipped in an aqueous solution including HF for a predetermined time, the exposed portion (D1) having the mixed structure of crystal phases is dissolved and then removed to thereby have a structure in FIG. 1D.
The above-described photosensitive glass substrate etching is a method of removing the exposed portion using the etching selectivity between the crystallized exposed portion and the unexposed portion, and, in particular, the method of removing the exposed portion thus described is referred to as positive etching. The above positive photosensitive glass substrate etching is widely utilized in forming a barrier lib of FED, PDP and PALC and an exposure of an inkjet head. It is also possible to form a hole with a diameter of 60 xcexcm on a glass substrate with a thickness of 200 xcexcm using the positive photosensitive glass substrate etching.
However, in the positive photosensitive glass substrate etching, there is a disadvantage that it is difficult to obtain a microstructure of a desired shape if the deposition degree of crystal phases at the exposed portion is not sufficient, so that heat treatment and etching have to be repeated in order to deposit sufficient crystal phases, thus making the process complicated and requiring a lot of time, although the method has an advantage that it is less expensive. That is, in a case where the percentage of crystal phases is about 25% in the structure of the exposed portion, the etching selectivity between the. exposed portion and the unexposed portion is not high, so that the exposed portion is not etched well and thus residuals remain at the exposed portion. Therefore, in case of manufacturing a microstructure having a high aspect ratio, there arises a problem that it is difficult to form a hole of a uniform size and the shape of a side wall of the microstructure is distorted.
Accordingly, there arises a problem that it is difficult to manufacture a microstructure with high reliability. In addition, the thermal expansive coefficient of a microstructure using a photosensitive glass substrate in the conventional art is about 7.5xc3x9710xe2x88x926. Generally, the microstructure is adhered to the substrate or a dielectric layer having a natural thermal expansive coefficient. However, the thermal expansive coefficient of glass most frequently used as a substrate for a flat panel display is 8.3xcx9c8.6xc3x9710xe2x88x926 in general. In case of a metal substrate frequently used as a material replacing the glass recently has a higher thermal expansive coefficient. Therefore, in a case where the difference in thermal expansive coefficient between the microstructure and the substrate to. be adhered to the microstructure, the. adhesion is not easily performed and there is a possibility that the microstructure or the substrate could be damaged.
Accordingly, it is an object of the present invention to provide a method of manufacturing a microstructure having a high aspect ratio.
It is another object of the present invention to provide a method of manufacturing a microstructure with high reliability in which no residuals remains after etching.
It is another object of the present invention to provide a method of manufacturing a microstructure by only one exposure and heat treatment by increasing the etching selectivity between an exposed portion and an unexposed portion.
It is another object of the present invention to provide a method of manufacturing a microstructure by which the step for controlling the thermal expansive coefficient of the microstructure in order to match with the thermal expansive coefficient of other materials is additionally carried out.
The method of manufacturing a microstructure in accordance with the present invention includes the steps for: forming a mask pattern on a photosensitive glass substrate; exposing the photosensitive glass substrate at an energy of 20J/cm2; changing an unexposed portion of the photosensitive substrate to a crystalline structure by removing the mask pattern and heat-treating the photosensitive glass substrate to a predetermined temperature; and removing the unexposed portion by selectively etching the same.
Additional advantages, objects and features of the invention will become more apparent from the description which follows.